Debugging With eMS CMS Debugging Commands
This section describes the debug tools that CMS provides. These tools can be used
to help you debug CMS or a problem program. In addition, a CMS user can use
the CP commands to debug. Information that is often useful in debugging is also
included. The following topics are discussed in this section: CMS debugging commands
Load maps • Reading CMS dumps • Control block summary CMS provides two commands that are useful in debugging: DEBUG and SVCTRACE. Both commands execute from the terminal.
The debug environment is entered whenever:
The DEBUG command is issued
A breakpoint is reached
An external or program interrupt occurs CMS will not accept other commands while in the debug environment. However,
while in the debug environment, subcommands of the DEBUG command can be
used to: • Set breakpoints (address stops) that stop program execution at specific
locations.
Display the contents of the CAW (channel address word), CSW (channel sta­
tus word), old PSW (program status word), or general registers at the terminal.
Change the contents of the control words (CAW, CSW, and PSW) and general
i
registers. • Dump all or part of virtual storage at the printer. • Display the contents of up to 56 bytes of virtual storage at the terminal. • Store data in virtual storage locations.
Allow an origin or base address to be specified for the program.
Assign symbolic names to specific storage locations.
Close all open files and I/O devices and update the master file directory.
Exit from the debug environment.
The SVCTRACE command records information for all SVC calls. When the trace
is terminated, the information recorded up to that point is printed at the system
printer.
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DEBUG
In addition, several CMS commands produce or print load maps. These load maps
are often used to locate storage areas while debugging programs.
The DEBUG command provides support for debugging programs at a terminal.
The virtual machine operator can stop the program at a specified location in order
to examine and alter virtual storage, registers, and various control words. Once CMS is in the debug environment, the virtual machine operator can issue the vari­
ous DEBUG subcommands. However, in the debug environment, all of the other CMS commands are considered invalid.
Any DEBUG subcommand may be entered if eMS is in the debug environment
and the keyboard is unlocked. The following rules apply to DEBUG
subcommands:
1. No operand should be longer than eight characters. All operands longer than
eight characters are left-justified and truncated on the right after the eighth
character.
2. The DEFINE subcommand must be used to create all entries in the DEBUG
symbol table.
3. The DEBUG subcommands can be truncated. The following is a list of all val­
id DEBUG subcommands and their minimum truncation.
Subcommand
BREAK
CAW CSW DEFINE
DUMP GO GPR
HX ORIGIN PSW RETURN SET STORE X
Minimum
Truncation
BR
CAW CSW DEF DU GO GPR
HX OR PSW RET SET ST X One way to enter the debug environment is to issue the DEBUG command. The
message
DMSDBG728I DEBUG ENTERED
appears at the terminal. Any of the DEBUG sub commands may be entered. To
continue normal processing, issue the RETURN subcommand. Whenever a pro­
gram check occurs, the DMSABN routine gains control. Issue the DEBUG com­
mand at this time if you wish CMS to enter the debug environment.
Whenever a breakpoint is encountered, a program check occurs. The message
DMSDBG728I DEBUG ENTERED BREAKPOINT YY AT XXXXX
526 VM/SP System Programmer's Guide